add support for hardware rtc, not sure if this version won't crash

src/rtc.cpp

@@ -0,0 +1,58 @@
+#include "rtc.hpp"
+
+bool rtcset;
+bool NTPupdated;
+
+ESP32Time rtc(0);
+bool rx_rtc_avail = false;
+RX8010SJ::Adapter rx_rtc = RX8010SJ::Adapter(RX8010SJ_ADDRESS);
+
+void timeToDateTime(time_t t, struct RX8010SJ::DateTime* dateTime) {
+    struct tm* timeinfo = gmtime(&t);
+    dateTime->second = timeinfo->tm_sec;
+    dateTime->minute = timeinfo->tm_min;
+    dateTime->hour = timeinfo->tm_hour;
+    dateTime->dayOfWeek = (timeinfo->tm_wday + 6) % 7;
+    dateTime->dayOfMonth = timeinfo->tm_mday;
+    dateTime->month = timeinfo->tm_mon + 1; // tm_mon is 0-11, convert to 1-12
+    dateTime->year = (timeinfo->tm_year + 1900) % 100; // Get last 2 digits
+}
+
+time_t timegm(struct tm *tm) {
+    // https://linux.die.net/man/3/timegm
+    time_t ret;
+    char *tz;
+
+    tz = getenv("TZ");
+    setenv("TZ", "", 1);
+    tzset();
+    ret = mktime(tm);
+    if (tz) setenv("TZ", tz, 1);
+    else unsetenv("TZ");
+    tzset();
+    return ret;
+}
+
+time_t dateTimeToTime(const struct RX8010SJ::DateTime* dateTime) {
+    struct tm timeinfo;
+    timeinfo.tm_sec = dateTime->second;
+    timeinfo.tm_min = dateTime->minute;
+    timeinfo.tm_hour = dateTime->hour;
+    timeinfo.tm_mday = dateTime->dayOfMonth;
+    timeinfo.tm_mon = dateTime->month - 1;
+    timeinfo.tm_year = dateTime->year + 100;
+    timeinfo.tm_isdst = 0;
+    return timegm(&timeinfo);
+}
+
+void sync_to_rx_rtc(int32_t offset) {
+    if(!rx_rtc_avail) return;
+    RX8010SJ::DateTime rx_currenttime = RX8010SJ::DateTime();
+    timeToDateTime(rtc.getEpoch() + offset, &rx_currenttime);
+    rx_rtc.writeDateTime(rx_currenttime);
+}
+void sync_from_rx_rtc(int32_t offset) {
+    if(!rx_rtc_avail) return;
+    RX8010SJ::DateTime dateTime = rx_rtc.readDateTime();
+    rtc.setTime(dateTimeToTime(&dateTime) + offset);
+}